This document describes how to use Open vSwitch with Libvirt 0.9.11 or later.
This document assumes that you followed Open vSwitch on Linux, FreeBSD and NetBSD or
installed Open vSwitch from distribution packaging such as a .deb or .rpm. The
Open vSwitch support is included by default in Libvirt 0.9.11. Consult
www.libvirt.org for instructions on how to build the latest Libvirt, if your
Linux distribution by default comes with an older Libvirt release.

The interface type must be set to bridge. The <source> XML element
specifies to which bridge this interface will be attached to. The
<virtualport> element indicates that the bridge in <source> element is
an Open vSwitch bridge.

Then (re)start the VM and verify if the guest’s vnet interface is attached to
the ovsbr bridge:

If the VM does not want to start, then try to run the libvirtd process either
from the terminal, so that all errors are printed in console, or inspect
Libvirt/Open vSwitch log files for possible root cause.